Burner for tube firing



June 18, 1957 M. J. PARKER ET AL BURNER FOR TUBE FIRING Filed July 21, 1954 2 Sheets-Sheet l H Ar 09mins.

June 18, 1957 M. J. PARKER ETAL BURNER FOR TUBE FIRING 2 She'eps-Sheet 2 Filed July 21, 1964 United States Patent BURNER FOR TUBE FIRING Melvin J. Parker, New York, and Alexander J. Turpin,

Stewart Manor, N. Y., assignors to Hauck Manufacturing Co., Brooklyn, N. Y., a corporation of New York Application July 21, 1954, Serial No. 444,782

13 Claims. (Cl. 158-11) This invention relates to burners for fluid fuel, and more particularly for firing into a long tube.

It is already known to burn gas in a burner firing into a tube. Such a tube may be made of a special high temperature alloy in order to operate at red heat corresponding to a temperature of 1,800 or 1,900 F., the tube then being used for radiant heating. In other cases the burner may fire into an immersion tube, and in still others it may fire into a finned tube for convection heating.

The radiant tube is the most common in use compared to immersion or convection tubes. A single furnace may have as many as forty radiant tubes, with forty burners, such a furnace being filled with an inert gas, for the bright annealing of steel. With radiant heating there are no flue gases in the furnace to spoil the desired bright finish. In the present specification these tubes, whether radiant, immersion or convection, will be referred to generically as a heater tube, for although heated by the burner flame, they are themselves used to heat something else.

The heater tube may be straight, or reversely bent to U shape, or doubly reversely bent to W shape, or curved to O shape, etc. In all cases the burner is disposed in one end of the tube, and hot gases are discharged at the other end, and ordinarily the ends will pass through and be supported by appropriate masonry. The primary object of the present invention is togenerally improve burners for such tube firing.

It will be evident that for tube firing the burner should produce an elongated slender flame. Some success has been achieved in this when burning gas, but not when buring liquid fuel or oil. One primary object of the present invention is to provide an oil burner which will produce a long slender flame. We have found that this may be done by whirling the secondary air, and the effect is precisely the opposite of what has heretofore been anticipated, for in an ordinary furnace burner, the air is whirled to produce a short flame. We have found to the contrary that in tube firing the whirled air produces a lengthened flame.

A further object is to provide means for controlling or adjusting the flame length, and this is readily accomplished by controlling the whirling of the secondary air. For this purpose an angularly adjustable deflecting vane may be positioned at the secondary air connection, with a control lever and a dial or scale, but the markings on the scale are in opposite direction to what would be expected on a furnace burner.

spaced therefrom to provide an annular passage around the primary air nozzle for the flow of a portion of the secondary air. We have also found it desirable to give the-flame retention nozzle a length ranging from one and 2,796,]. 18 Patented June 18, 1957 a half to two and a half times its diameter. The diameter is intermediate the diameters of the primary air tube, and the heater tube in which the burner is to operate.

Still another object of the present invention is to provide a combination burner which will burn either gas or oil, and which is readily and quickly changed from one fuel to the other.

To accomplish the foregoing general objects and other more specific objects which will hereinafter appear, our invention resides in the combination burner elements, and their relation one to another and to the heater tube, as are hereinafter more particularly described in the following specification. The specification is accompanied by drawings, in which:

Fig. 1 is a longitudinal section through a combination burner embodying features of our invention;

Fig. 2 is a schematic view showing the burner applied to a U tube and arranged to burn oil;

Fig. 3 is a similar view showing the burner applied to a W tube and arranged to burn either oil or gas;

Fig. 4 is a plan view of the burner;

Fig. 5 is a section taken approximately in the plane of the line 5-5 of Fig. 1;

Fig. 6 is a fragmentary vertical section similar .to a part of Fig. 1, but drawn to enlarged scale;

Fig. 7 is a section taken in the plane of the line 77 of Fig. 6, but drawn to reduced scale; and V Fig. 8 is a section through the oil tip taken in the plane of the line 88 of Fig. 6.

Referring to the drawing, and more particularly to Fig. 2, we there show a heater tube 12 of the reversely bent or U type. This may be made of a heat resistant alloy steel for operation as a radiant heater. Theentrant end 14 of the tube passes through a suitable masonry or fire brickor like heat resistant wall 16. The discharge end 18 of the tube leads to asuitableflue here indicated at 20. The rear end of theburner is generally designated B, and it is secured to the entrant end of heater tube 14 by means of appropriate set screws 22. Oil or liquid fuel is supplied to the burner through a pipe 24, and may be shut off by a valve 26. The amount of oil flow is controlledby a suitable knob 28, having a pointer 3.0 coopcrating with a scale at 32. Primary air is supplied through a pipe 34, preferably having a valve 36, and secondary air is supplied through a pipe 38, preferably having a valve 40. High voltage electricity for ignition purposes may be supplied at a pair of insulated terminals 42.

The primary air is an atomizing air, and may be used at a pressure of say 16 oz. The secondary air is combustion air, and may be used at a lower pressure of, say, 8 oz. However, in many installations a single blower is used for both, and the combustion air is therefore received at ahigher pressure, the same as the primary air. The primary air valve 36 is for shut off when removing ,a burner for service. There is ordinarily no regulation of the amount of primary air. However, the valve 40 may be used to regulate the amount of secondary or cornbustion air, or in the case of a bank of burners, there may be a single automatic control valve which controls an entire bank of burners.

'Fig. 3 is generally similar to Fig. 2, but shows a heater tube 50 which is doubly reversely bent, or a socalled W tube. Hereagain the tube is mounted inand passes through a suitable fire brick wall 52. The inlet end 54 of the heater tubereceivesthe burner .B, vwhile the discharge end .56.may be connected .to a suitable flue 58. In this case the burner has not only an oil supply pipe 60, a primary air pipe 61 and secondary air pipe 64, but also a gas supply pipe 66. The gas maybe regulated by means of a valve 68. When gas' is used the valve 62 is shut, and no primary 'air' is'.used, because no atomization is needed. The valve- 70 is a three-way valve which connects either one of two inlets to a common outlet, with the other inlet shut oif.

The showing in Figs. 2 and 3 is schematic rather than practical, for with vertical air supply pipes as shown, the U and W heater tube would commonly be disposed in a horizontal plane, with both legs of equal length. With the U or W tube disposed in a vertical plane as shown, the air supply pipes would ordinarily run horizontally. Therefore, in Figs. 2 and 3 the projection of the burner leg of the heater tube is exaggerated, and would ordinarily be a matter of only three or four inches from the fire wall, affording enough room to work with a wrench.

The burner may be described with reference first to Fig. 1 of the drawing. It comprises an oil tube 72 terminating at its inner end in an oil tip 74. A primary air tube 76 surrounds the oil tube 72, and terminates in a primary air nozzle 78, located at the oil tip 74. There is also a connection or cast body generally designated 80 for a supply of secondary air to flow outside the primary air tube 76 and within the heater tube 82 within which the burner is to be used. The burner further comprises a flame retention nozzle 84 (also called a firing nozzle or an ignition nozzle), the said nozzle being closed at its rear end by a plate 86 (Figs. 6 and 7) which plate surrounds the primary air nozzle 78, but is radially spaced therefrom to provide an annular passage 88 immediately around the primary air nozzle 78. This affords flow of a portion of the secondary air around the nozzle 78 and within the flame retention nozzle 84.

It will be seen that the nozzle 84 has a diameter substantially larger than that of the primary air tube 76, and substantially smaller than that of the heater tube 82. The main body of secondary air flows outside the flame retention nozzle 84, and adjacent the inner wall of the heater tube 82 (Fig. l). Reverting to Fig. 6, the plate 86 supports the flame retention nozzle 84, and is itself supported by the primary air tube 76. For this purpose the latter is surrounded by a suitable collar 90, and the parts 86 and 90 are connected by a number of thin webs 92. In the present case there are three such webs, as is best shown in Fig. 7, but there may be more. Moreover, in Fig. 6 it will be seen that the webs are cut away adjacent the primary air nozzle 78 until they reach back all the way to the collar 90. Thus the desired annular passage 88 for flow of secondary air around the outside of the primary air nozzle 78 is not interrupted, not even by the three webs 92.

The annular passage around the primary air nozzle may have a width of from /s" to A" in radial direction, on a nozzle 1% in diameter. The continuous passage has the advantage of avoiding turbulence and eddy currents inside the flame retention nozzle, which otherwise would be caused by the disharge of the primary air. Heretofore, the latter would cause a vacuum at the back of the flame retention nozzle, but with our construction the vacuum is satisfied by the secondary air flowing smoothly through the annular passage. For best result the passage should be a continuous annular passage, and it should be located immediately around the primary air nozzle, and it should also be close to the primary air nozzle in axial direction, though not critically so, for a spacing of one or a few inches is permissible.

The cylindrical portion 84 of the flame retention nozzle is secured to the support plate 86 around its flange 94 by means of a plurality of screws 96 shown in Figs. 1 and 4. The cylindrical portion 84 is preferably given a length ranging from one and a half to two and a half times its diameter.

Referring now to Figs. 1 and 5, the secondary air body 80 preferably has means to cause the secondary air to whirl, that is, to take a helical path. In the present case it is provided with an angularly adjustable deflecting vane 100. This is carried by a pin 102 having a control conventional marking for furnace burners, in which whirled air produces a shortened flame. If increased deflection reduces the air and causes smoke, the valve 40 is opened enough to restore sumcient air.

In Fig. 1 it will be seen that the secondary air flows through an annular passage 106 outside the primary air tube 76, and then follows a helical path in the space between the primary air tube 76 and the heater tube 82. The burner has considerable overall length, and this aifords time for the whirling air to move outward under centrifugal force, so that it tends to hug the outer wall in its travel. While not certain of the explanation, it is our theory that this slows and delays the admixture of the secondary air with the fuel and primary air discharged from the nozzle 78, and thus makes it possible to greatly prolong the burning of the fuel, and to correspondingly elongate the flame.

One feature of the present burner is that the secondary or combustion air is released far back of the ignition point, and is released into a large chamber, so that it can assume a smooth streamlined flow, and would be guided outward around the flame retention nozzle even if there were no whirl. However, the whirl helps delay combustion, and this produces a longer flame. Either way, there is a minimum eddy current and tubulence.

With the present burner no diificulty is experienced in elongating the flame until it projects from and is readily visible well beyond the discharge end of a radiant tube twenty feet or more in length. Moreover, the distribution of heat is controllable, and if desired the heater tube may be given a lower temperature in the portion following the burner than in parts of the tube more remote from the burner. The length of the flame is readily controlled by changing the angle of the deflecting vane 100.

Referring to Fig. l, the oil supply line is connected to the burner at a suitable tapped hole and then flows through the oil tube 72. It first passes a regulating valve which is controlled by knob 28 having an indicator 30, which in turn cooperates with an arcuate scale on the face 112. The valve per se'is not shown but may be conventional. The valve handle 28 may be used to shut oil? the oil flow entirely, but an additional valve 26 is provided in the supply line 24, as shown in Fig. 2, for convenience in servicing, as well as to insure safe cut off when working with gas.

When burning gas the oil tip 74 is retracted relative to the primary air nozzle 78. The oil tip may vary, but in the present case has tangential holes, as is best shown in Fig. 8. It is supported in concentric relation to the nozzle 78 by suitable centering pegs, best shown at 114 in Fig. 6. These pegs are axially slidable inside nozzle 78.

At the rear end of the burner the oil tube 72 is received in a fitting 116 which is axially slidable in body 118, and its position is locked by means of one or more set screws 122. A special safety screw 124 may be provided, which is not loosened or removed, but which functions to limit the motion of part 116 out-of body 118. Stop screw 124 is slidably received in a slot similar to that receiving the set screw 122, andby loosening the set screw 122, the end portion 112 of the burner may be pulled outwardly as far as permitted by stop screw 124, and the screw 122 again tightened. This simple step converts the burner from oil to gas, it being understood .that the oil tube 72 and oil tip 74 all move rearward with the part 112 of the burner. g

A burner sold for use with oil only is sold as shown, because permitted simplification is too minor to be worth making. A burner intended for use with gas only is simplified to reduce cost by removing the oil tube, oil tip, and control valve, and instead closing the primary air body 118 by means of a suitable plug replacing the part 116, and preferably having an observation port.

The primary air body 118 is itself received within the secondary air body 80. The latter may include an orifice plate 128 which limits the flow of secondary air. Secondary air body 80 has an annular portion which is received in a mounting bracket 130, which in turn carries an adapter ring 132 having a plurality, in this case, three ears 134, each having a screw 136. As will be clear from inspection of Figs. 1 and 4, the screws 136 serve to secure the burner to the entrant end of the heater tube 82. If the burner is to be serviced the mounting bracket 130 may be separated from the adapter ring 132 by releasing a number of holding'screws, shown at 138 in Fig. 4, whereupon the entire burner may be pulled bodily out of the heater tube for inspection and service.

The burner may be ignited in conventional fashion by means of a pair of electrodes to which high tension electric current is supplied. Specifically there are terminals 42 (Fig. 4) having insulation bodies 140 (Fig. 1) somewhat resembling a spark plug and similarly screwed through threaded openings in the mounting bracket 130. At their lower ends the upright conductors of the terminals are connected to horizontal rods 142, which in turn pass through cylindrical insulators 144, held in position by a clamp plate 146 and screw 148. The insulators pass through the annular support plate 86 of the flame retention nozzle 84, and carry electrodes 150 which come close together at their tips, as is best shown in Fig. 4. It will be noted (Fig. 7) that the insulators 144 are spaced from the primary air nozzle 78 high enough to avoid interruption of the desired annular sleeve of secondary air entering the flame retention nozzle immediately around the primary air nozzle. We believe that the continuous sleeve of air here provided reduces and almost eliminates carbon formation, and results in a better shape of flame and control of flame within the flame retention nozzle 84.

The burner may be provided with an observation port, and this is shown at 152 in Fig. 1. It includes a transparent window 154 held in place by the hollow port 152. Small screw plugs 156 shown beneath the primary and secondary air connections are for convenience in connecting a pressure gauge or manometer to the burner.

The threaded connections at the top of the primary and secondary air bodies are flange connections, which are bolted to the body, as shown at 164 and 166 in Fig. 4. The orifice plate 128 (Fig. 1) is simply bolted between the flanged parts, as is also shown in Fig. 5. The plate may be preliminarily secured to the upper part by small screws, as shown in Figs. 1 and 5.

One of the manufacturing advantages of the arrangement here disclosed will be apparent from inspection of Fig. 1. The overall length of the burner may be varied while using standard parts at each end of the burner. It is only necessary to change the length of the oil tube 72, the primary air tube 76, and the electrode connecting rods or wires 142. In practical service this is an important advantage because different installations require different overall length of burner. In all cases it is desirable that the flame retention nozzle 84 reach the inner face of the masonry or fire brick wall, as shown in Fig. 1 of the drawing. This is so because the heater tube 82 should not be exposed on the inside to flame and heat, at a point where there would be no immediate and effective dissipation of heat from the outside. Thus the thickness of the masonry wall 160 will itself be a factor determining the minimum length of burner. Other factors may enter into particular installations, such as the room required for making pipe connections, and the nature of the flue connection at thedischarge ends of the heater tubes when the tubes are of thefU or W type.

It is believed that the construction and operation of our improved burner for tube firing, as well as the advantages thereof, will be apparent from the foregoing detailed description. The burner is made in several sizes, corresponding to large changes in diameter of heater tube. The specific burner shown is intended to burn from one-half to three gallons of oil per hour, and would ordinarily be used in aheater tube ranging in diameter from three and one-half inches to five inches. A larger radiant tube would require a greater oil consumption and a larger burner. To accommodate a range of heater tube diameter for a specific burner size it is merely necessary to change the adapter ring 132 shown in Figs. 1 and 4. Moreover, each burner size may be supplied in different lengths, depending on the requirements of the purchaser, and a change in length is readily accom modated at the factory, as previously explained.

The present burner produces a long slender flame, which may be made as long as the heater tube in which it is used. The length of flame is readily controllable at the burner by modifying the degree of whirl of the secondary air. The burner is successful with oil as well as with gas, and indeed the change needed in going from one fuel to the other is so slight that the burner is preferably made as a combination burner which may be used with either fuel. When burning oil the oil tip is kept in the forward or inner position, shown in Figs. 1 and 6. When burning gas the oil tip is pulled back to rear or outer position, and the gas is fed into the primary air body and replaces the primary air supply. In a growing number of installations both oil and gas are provided, the oil being used to overcome seasonal fluctuations in the availability and price of gas.

The present burner ignites easily and quietly, with no initial oil accumulation and explosion. The formation of carbon is minimized. There is no need to preheat the primary or secondary air, and there is no need to use high pressure air. The burner works fully successfully with unheated air, and with direct atomization produced by means of low pressure air or blower air. The great length of the burner affords ample opportunity for the whirling air to move outward by centrifugal force before reaching the combustion zone, and contrary to prior experience with furnace burners, increased whirl lengthens rather than shortens the flame.

It will be understood that while we have shown and described our invention ina preferred form, changes may be made in the structure shown, without departing from the scope of the invention, as sought to be defined in the'following claims. In the claims the term oil has been used for convenience, but is intended to apply to liquid fuels in contradistinction to gaseous fuels. In the claims We have for convenience referred to theprimary air tube and primary air nozzle, but this is not intended to exclude the burning of gas, at which time there would be no-primary air. Similarly we havefor convenience referred to the secondary air body and to secondary air flow, although it will be understood that when burning gas, the so-called secondary air really will be the'only air used. Also, we have referred to the rear end of the nozzle as a plate, but it could take many forms, and even as here shown it has radial support webs and a flange and is not truly plate-like. Moreover, it is obvious that it could be integral with the cylindrical sleeve of the nozzle.

We claim:

1. In combination, a heater tube 'whichis very long compared to its diameter and which is non-insulated and adapted to be used as a heat exchanger for providing intentional transfer of heat through thetube wall, and a burner having forward and rear portionsand a central tubetherebetween, the forward portion of said burner being smaller in diameter than the heater tube and being inserted longitudinally of said tube directly intoone end of said tube for firing said tube, said heater tube terminating inan outlet at its other end, the forward end of said burner having a flame retention means, said burner comprising a fuel connection through said central tube and a combustion air connection located near the rear end of the burner for supplying combustion air to the space between the central tube and the heater tube, said central tube being designed to afford a straight flow therethrough, and said burner having means to whirl the combustion air around the tube and cause it to assume a helical path as it moves forward around the outside of the central tube and beyond the burner, and thereby delaying admixture with the fuel in order to prolong the flame for more uniform heating of the heater tube along its length, the forward portion of said burner being designed to direct all of the fuel forwardly to contribute to the aforesaid desired prolongation of flame.

2. In combination, a heater tube which is very long compared to its diameter and which is non-insulated and adapted to be used as a heat exchanger for providing intentional transfer of heat through the tube wall, and a relatively long burner having forward and rear portions a and a central tube therebetween, the forward portion of said burner being smaller in diameter than the heater tube and being inserted longitudinally of said tube directly into one end of said tube for firing said tube, said heater tube treminating in an outlet at its other end, the forward'end of said burner having a flame retention means, said burner comprising a fuel connection through said central tube and a combustion air connection located near the rear end of the burner for supplying combustion air to the space between the central tube and the heater tube, said central tube being designed to afford straight flow therethrough, an angularly adjustable deflecting vane at the combustion air connection together with control means to adjust the angle of said vane, said vane serving to whirl the combustion air around the tube and cause it to assume a helical path as it moves forward around the outside of the central tube and beyond the burner, and thereby delaying admixture with the, fuel in order to prolong the flame for more uniform heating of the heater tube along its length, the control means for said vane including a scale indicating an increase in flame length for an increase in vane angle, and vice versa, the forward portion of said burner being designed to direct all of the fuel forwardly to contribute to the aforesaid desired prolongation of flame.

3. In combination, a heater tube which is very long compared to its diameter and which is non-insulated and adapted to be used as a heat exchanger for providing intentional transfer of heat through the tube wall, and a burner having forward and rear portions and a central tube therebetween, the forward portion of said burner being smaller in diameter than the heater tube and being inserted longitudinally of said tube directly into one end of said tube for firing said tube, said heater tube terminating in an outlet at its other end, the forward end of said burner having a flame retention means, the rear end of said burner comprising connections for fluid fuel and primary and secondary air, said central tube being designed to afford a straight flow therethrough and terminating in a nozzle designed to direct the fuel axially forward, means to deliver fuel into said central tube for emission from said nozzle, means whereby the secondary air connection leads to the space between the central tube and the heater tube, means to cause the secondary air to whirl around the tube and take a helical path around the outside of the central tube and beyond the burner in order to prolong the flame for more uniform heating of the heater tube along its length, and means to adjust the degree of whirl in order to control the length of flame, the forward portion of said burner being designed to direct all of the fuel forwardly to contribute to the aforesaid desired prolongation of flame.

4. In combination, a heater tube which is very long compared toits diameter and which is non-insulated and adapted to be used as a heat exchanger for providing intentionaltransfer of heat through the tube wall, and a burner having forward and rear portions and a central tube therebetween, the forward portion of said burner being smaller in diameter than the heater tube and belng inserted longitudinally of said tube directly into one end of said tube for firing said tube, said heater tube terminating in an outlet at its other end, the forward end of said burner having a flame retention means, the rear end of said burner comprising connections for fluid fuel and primary and secondary air, said central tube being arranged to receive said fuel and primary air and being designed to afford a straight flow therethrough and terminating in a nozzle designed to direct the fuel axially forward, means whereby the secondary air connection leads to the space between the central tube and the heater tube, an angularly adjustable deflection vane associated with said secondary air connection to guide the secondary air tangentially and to cause the same to whirl around the tube and take a helical path around the outside of the central tube and beyond the burner in order to prolong the flame for more uniform heating of the heater tube along its length, and means to adjust the vane angle in order to control the length of flame, said means including a scale indicating an increase in flame length for an increase in vane angle and vice versa, the forward portion of said burner being designed to direct all of the fuel forwardly to contribute to the aforesaid desired prelongation of flame.

5. In combination, a heater tube which is very long compared to its diameter and which is non-insulated and adapted to be used as a heat exchanger for providing intentional transfer of heat through the tube wall, and a burner having forward and rear portions and a central tube therebetween, the forward portion of said burner being smaller in diameter than the heater tube and being inserted longitudinally of said tube directly into one end of said tube for firing said tube, said heater tube terminating in an outlet at its other end, said central tube being designed to afford a straight flow therethrough, and terminating in a primary nozzle designed to direct the fuel axially forward, means to deliver fuel into said central tube for emission from said primary nozzle, a connection near the rear end of the burner for a supply of combustion air to flow outside the central tube between the central tube and the heater tube, a flame retention nozzle having a diameter larger than the central tube and smaller than the heater tube, said flame retention nozzle being closed at its rear end by a plate surrounding the primary nozzle but radially spaced therefrom to provide an annular passage around the primary nozzle for the flow of a portion of the combustion air, and an angularly adjustable deflecting vane at the combustion air connection to whirl the combustion air around the tube in a helical path around the outside of the central tube and beyond the burner in order to prolong the flame for more uniform heating of the heater tube along its length, the forward portion of said burner being designed to direct all of the fuel forwardly to contribute to the aforesaid desired prolongation of flame.

6. In combination, a heater tube which is very long compared to its diameter and which is non-insulated and adapted to be used as a heat exchanger for providing intentional transfer of heat through the tube wall, and a burner having forward and rear portions and a primary air tube therebetween, the forward portion of said burner being smaller in diameter than the heater tube and being inserted longitudinally of said tube directly into one end of said tube for firing said tube, said heater tube terminating in an outlet at its other end, said burner comprising an oil supply tube terminating at its forward end in an oil delivery tip, said primary air tube surrounding said oil supply tube and terminating in a primary air nozzle at said oil delivery tip, said tip and nozzle being designed to direct the fuel axially forward, means near the rear end of the burner to supply primary air to said primary air tube, a connection near the rear end of the burner to supply secondary air to the space between the primary air tube and the heater tube, a flame retenstion nozzle having a diameter larger than the primary air tube and smaller than the heater tube, said flame retention nozzle being closed at its rear end by a plate surrounding the primary air nozzle but radially spaced therefrom to provide an annular passage around the primary nozzle for the flow of a portion of the secondary air, said central tube being designed to afford a straight flow therethrough, and an angularly adjustable deflecting Vane at the secondary air around the tube connection to whirl the secondary air in a helical path around the outside of the primary air tube and beyond the burner in order to prolong the flame for more uniform heating of the heater tube along its length, the forward portion of said burner being designed to direct all of the fuel forwardly to contribute to the aforesaid desired prolongation of flame.

7. In combination, a heater tube which is very long compared to its diameter and which is non-insulated and adapted to be used as a heat exchanger for providing intentional transfer of heat through the tube wall, and a burner having forward and rear portions and a primary air tube therebetween, the forward portion of said burner being smaller in diameter than the heater tube and being inserted longitudinally of said tube directly into one end of said tube for firing said tube, said heater tube terminating in an outlet at its other end, the forward end of said burner having a flame retention means, said primary air tube terminating in an air nozzle, a primary air connection to the rear end of said primary air tube, said central tube being designed to afford a straight flow therethrough, means to deliver fuel into said primary air tube, said nozzle being designed to direct the fuel axially forward, a secondary air connection located near the rear end of the primary air tube for supplying secondary air to the space between the primary air tube and the heater tube, an angularly adjustable deflecting vane at the secondary air connection together with control means to adjust the angle of said vane, said vane serving to Whirl the secondary air around the tube and cause it to assume a helical path as it moves around the outside of the primary air tube and beyond the burner, thereby delaying admixture with the fuel and primary air in order to prolong the flame for more uniform heating of the heater tube along its length, the forward portion of said burner being designed to direct all of the fuel forwardly to contribute to the aforesaid desired prolongation of flame.

8. In combination, a heater tube which is very long compared to its diameter and which is non-insulated and adapted to be used as a heat exchanger for providing intentional transfer of heat through the tube Wall, and a burner having forward and rear portions and a primary r air tube therebetween, the forward portion of said burner being smaller in diameter than the heater tube and being inserted longitudinally of said tube directly into one end of said tube for firing said tube, said heater tube terminating in an outlet at its other end, the forward end of said burner having a flame retention means, said burner comprising an oil supply tube terminating at its inner end in an oil delivery tip, said primary air tube surrounding said oil tube and terminating in a primary air nozzle at said oil delivery tip, said tip and nozzle being designed to direct the fuel axially forward, a primary air connection to the rear end of the primary air tube, said central tube being designed to afford a straight flow therethrough, a secondary air connection located near the rear end of the primary air tube for supplying secondary air to the space between the primary air tube and the heater tube, an angularly adjustable deflecting vane at the secondary air connection together with control mean to adjust the angle of said vane, said vane serving to Whirl the secondary air around the tube and cause it to assume a helical path as it moves around the outside of the primary air tube and beyond the burner, thereby delaying admixture with the fuel and primary air in order to prolong the flame for more uniform heating of the heater tube-along its length, the forward portion of said burner being designed 10 to direct all of the fuel forwardly to contribute to th aforesaid desired prolongation of flame.

9. In combination, a heater tube which is very long compared to its diameter and which is non-insulated and adapted to be used as a heat exchanger for providing intentional transfer of heat through the tube Wall, and a burner having forward and rear portions and a central tube therebetween, the forward portion of said burner being smaller in diameter than the heater tube and being inserted longitudinally of said tube directly into one end of said tube for burning either oil or gas for firing said tube, said heater tube terminating in an outlet at its other end, said burner comprising an oil supply tube terminating in an oil delivery tip, said central tube surrounding the oil tube and terminating in a primary air and gas nozzle, said tip and nozzle being designed to direct the fuel axially forward, a flame retention nozzle secured to the central tube, said flame retention nozzle having a diameter larger than the central tube and smaller than the heater tube, said central tube being designed to afford a straight flow therethrough, a secondary air connection for supplying secondary air to the space between the central tube and the heater tube, an angularly adjustable deflecting vane at the secondary air connection to whirl the secondary air around the tube to assume a helical path around the outside of the central tube and beyond the burner in order to prolong the flame for more uniform heating of the heater tube along its length, a pipe connection to the central tube for receiving primary air when oil is burned, or gas when gas is burned, means affording axial movement of the oil tube and oil tip relative to the central tube and primary nozzle, and means to lock the oil tube in either forward position for oil burning or retracted position for gas burning, the

. forward portion of said burner being designed to direct all of the fuel forwardly to contribute to the aforesaid desired prolongation of flame.

10. In combination, a heater tube which is very long compared to its diameter and which is non-insulated and adapted to be used as a heat exchanger for providing intentional transfer of heat through the tube wall, and a burner having forward and rear portions and a central tube therebetween, the forward portion of said burner being smaller in diameter than said tube and being inserted longitudinally of said tube directly into one end of said tube for burning either oil or gas for firing said tube, said heater tube terminating in an outlet at its other end, said burner comprising an oil supply tube terminating at its forward end in an oil delivery tip, said central tube surrounding the oil tube and terminating in a primary air and gas nozzle at the oil delivery tip, said tip and nozzle being designed to direct the fuel axially forward, a connection for a supply of secondary air to flow in the space between the central tube and the heater tube, a flame retention nozzle having a diameter larger than the central tube and smaller than the heater tube, said flame retention nozzle being closed at its rear end by a plate surrounding the primary air nozzle but radially spaced therefrom to provide an annular passage around the primary air nozzle for the flow of a portion of the secondary air, said central tube being designed to affor a straight flow therethrough, an angularly adjustable defleeting vane at the secondary air connection to whirl the secondary air around the tube to assume a helical path around the outside of the central tube and beyond the burner in order to prolong the flame for more uniform heating of the heater tube along its length, a pipe connection to the central tube for receiving primary air when oil is burned, or gas when gas is burned, means affording axial movement of the oil tube and oil tip relative to the central tube and primary nozzle, and means to lock the oil tube in either forward position for oil burning or retracted position for gas burning, the forward portion of said burner being designed to direct all of the fuel forwardly to contribute to the aforesaid desired prolongation of flame.

11. In combination, a heater tube which is very long compared to its diameter and which is noninsulated and adapted to be used as a heat exchanger for providing intentional transfer of heat through the tube wall, and a burner having forward and rear portions and a central tube therebetween, the forward portion of said burner being smaller in diameter than the heater tube and being inserted longitudinally of said tube directly into one end of said tube for burning either oil or gas for firing said tube, said heater tube terminating in an outlet at its other end, said burner comprising an oil supply tube terminating in an oil delivery tip, said central tube surrounding the oil tube and terminating in a primary air and gas nozzle, said tip and nozzle being designed to direct the fuel axially forward, a flame retention nozzle secured to the central tube, said flame retention nozzle having a diameter larger than the central tube and smaller than the heater tube, a secondary air connection near the rear end of the burner for supplying secondary air to the space between the central tube and the heater tube, a pipe connection to the central tube near the rear end of the burner for receiving primary air when oil is burned, or gas when gas is burned, means affording axial movement of the oil tube and oil tip relative to the central tube and primary nozzle, and means to lock the oil tube in either forward position for oil burning or retracted position for gas burning.

12. In combination, a heater tube which is very long compared to its diameter and which is non-insulated and adapted to be used as a heat exchanger for providing intentional transfer of heat through the tube wall, and a burner having forward and rear portions and a central tube therebetween, the forward portion of said burner being smaller in diameter than the heater tube and being inserted longitudinally of said tube directly into one end of said tube for firing said tube, said heater tube terminating in an outlet at its other end, said central tube terminating in a primary nozzle designed to direct the fuel axially forward, means to deliver fuel into said central tube for emission from said primary nozzle, a connection near the rear end of the burner for a supply of combustion air to flow between the central tube and the heater tube, and a flame retention nozzle having a diameter larger than the central tube and smaller than but at least half the diameter of the heater tube in order to provide an annular secondary air passage, said flame retention nozzle being closed at its rear end by a plate surrounding the primary nozzle but radially spaced therefrom to provide a continuous annular passage around being smaller in diameter than the heater tube and being inserted longitudinally of said tube directly into one end of said tube for firing said tube, said heater tube terminating in an outlet at its other end, said burner comprising an oil supply tube terminating at its inner end in an oil delivery tip, said primary air tube surrounding said oil tube and terminating in a primary air nozzle at the oil delivery tip, said tip and nozzle being designed to direct the fuel axially forward, a connection near the rear end of the burner for a supply of secondary air to flow between the primary air tube and the heater tube, and a flame retention nozzle having a diameter larger than the primary air tube and smaller than but at least half the diameter of the heater tube in order to provide an annular secondary air passage, said flame retention nozzle being closed at its rear end by a plate surrounding the primary air nozzle but radially spaced therefrom to provide a continuous annular passage around the primary nozzle for the flow of a portion of the secondary air.

References Cited in the file of this patent UNITED STATES PATENTS 741,504 Kemp Oct. 13, 1903 821,419 Kemp May 22, 1906 871,656 Worthen Nov. 19, 1907 1,069,243 Fogler Aug. 5, 1913 1,316,021 Doble Sept. 16, 1919 1,923,330 Sallee Aug. 22, 1933 1,953,590 Cone Apr. 3, 1934 2,059,523 Hepburn et al. Nov. 3, 1936 2,090,740 Zimmerman Aug. 24, 1937 2,126,417 Sharp Aug. 9, 1938 2,516,063 Logan July 18, 1950 2,602,440 Corns July 8, 1952 2,673,726 Oldenkamp Mar. 30, 1954 2,682,302 Cote June 29, 1954 FOREIGN PATENTS 475,721 Great Britain Nov. 24, 1937 

